As illustrated in FIG. 1, imprint lithography is a process in which a mold 1 with a pattern P formed thereon is pressed against a sample 3 coated with an imprintable material 2 having plasticity and curability, whereby an inverted shape of the pattern P is transferred. In the imprint lithography, a thickness of a transferred pattern T formed upon transferring of a shape includes a portion called a residual film F, as illustrated in FIG. 2.
In the imprint lithography, the imprintable material 2 is used as a mask, which requires a process of removing the residual film F. In order to conduct the process of removing the residual film within a short period of time so as not to impair the quality of the mask, it is necessary to form the residual film F thinly and uniformly over the entire imprint region.
According to the imprint lithography, in the case where the sparseness and denseness of the pattern P is uniform, for example, as in patterned media and photonic crystals, it is easy to realize the uniform residual film F. However, in the case where the pattern P has varied sparseness and denseness as illustrated in FIG. 3, it is difficult to form the residual film F in the transferred pattern T uniformly. That is, in the pattern P of the mold 1, when a portion to be formed as a recess in the mold 1 is assumed to be a pattern and the pattern density is higher as the area of the pattern per given area is larger, a pattern on the right side in the figure becomes denser and a pattern on the left side in the figure becomes sparser. When the pattern P of the mold 1 is pressed against the imprintable material 2 with a uniform thickness, as illustrated in FIG. 3(b) from the state illustrated in FIG. 3(a), if the imprintable material 2 does not flow to other portions after entering each corner inside the pattern P, a thickness tR of the residual film F on the right side in the figure, which is a portion of a dense pattern, becomes smaller than a thickness tL of the residual film F on the left side in the figure, which is a portion of a sparse pattern. Thus, the thickness of the residual film F varies depending upon the density of the pattern.
The variation in thickness of the residual film depending upon the sparseness and denseness of a pattern is inevitably caused by the sparseness and denseness of an IC pattern when the pattern is created as an arbitrary circuit configuration with a general IC layout. Therefore, a residual film having different thicknesses is formed at all times, which makes it necessary to perform an operation of removing the residual film for a long period of time until a portion with a large thickness can be removed. This is a waste of time, and in addition, the shape of the thus-formed transferred pattern T is degraded conspicuously. Further, in the case where the non-uniformity of the residual film is large, there may be arose a situation in which the transferred pattern T itself that should remain may be removed. Further, a final residual film distribution can be made uniform, by using an imprintable material with a low viscosity and performing imprint for a longer period of time. However, for this purpose, it is necessary to use a mold and a substrate having ideal flatness, and the above-mentioned uniform state cannot be so expected without a process performed for a very long period of time.
Currently, as a process for forming a residual film uniformly with respect to an arbitrary pattern P, a process is proposed, in which an imprintable material is placed in a state of a number of liquid droplets in an imprint region, and the amount of the liquid droplets are adjusted according to the sparseness and denseness of the pattern at that time. However, this process, for example, requires a complicated mechanism and a limited material for the imprintable material. Thus, this process is not applicable to an arbitrary imprintable material.
Further, regarding the imprint lithography on a substrate uniformly coated with an imprintable material, for example, “Imprint lithography” disclosed in JP-A-2006-303503 (“JP-A” means unexamined published Japanese patent application) proposes that the pattern density is made uniform, for example, by introducing a step of averaging a pattern density in IC layout design, thereby adjusting appropriately the two-dimensional arrangement of a pattern.    Patent Document 1: JP-A-2006-303503